Loans - Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	$ 5,510,887	$ 4,907,076	$ 4,808,672
Commercial mortgages	3,077,172	2,800,760
Construction	642,992	426,639
Land	300,314	239,937
Total commercial real estate	4,020,478	3,467,336	3,370,969
Home equity loans	337,879	329,853
Home equity lines of credit	216,281	195,132
1-4 family residential mortgages	28,416	32,447
Construction	17,080	13,123
Other	247,412	237,649
Total consumer real estate	847,068	808,204	799,827
Total real estate	4,867,546	4,275,540
Consumer installment	384,931	350,827
Other	6,567	7,289
Total consumer and other	391,498	358,116	350,112
Unearned discounts	(23,147)	(25,032)	(23,126)
Total loans	10,746,784	9,515,700	9,306,454
Total commercial and industrial percentage of total loans	51.30%	51.60%
Commercial mortgages percentage of total loans	28.60%	29.40%
Construction percentage of total loans	6.00%	4.50%
Land percentage of total loans	2.80%	2.50%
Total commercial real estate percentage of total loans	37.40%	36.40%
Home equity loans percentage of total loans	3.10%	3.50%
Home equity lines of credit percentage of total loans	2.00%	2.10%
1-4 family residential mortgages percentage of total loans	0.30%	0.30%
Construction percentage of total loans	0.20%	0.10%
Other percentage of total loans	2.30%	2.50%
Total consumer real estate percentage of total loans	7.90%	8.50%
Total real estate percentage of total loans	45.30%	44.90%
Consumer installment percentage of total loans	3.60%	3.70%
Other percentage of total loans	0.00%	0.10%
Total consumer and other percentage of total loans	3.60%	3.80%
Unearned discounts percentage of total loans	(0.20%)	(0.30%)
Total loans percentage	100.00%	100.00%
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	5,188,609	4,587,499
Total commercial and industrial percentage of total loans	48.30%	48.20%
Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	$ 322,278	$ 319,577
Total commercial and industrial percentage of total loans	3.00%	3.40%